Containers of polyvinyl acetals



Patented Nov. 4, 1947 CONTAINERS OF POLYVINYL ACETALS Lloyd Lyn Leach,Swarthmore, Pa., assignor to E. I. du, Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationAugust 18, 1943, Serial No. 499,115

Claims.

' "This invention relates to the packaging of commodities such asground, roasted coffee, which deteriorate rapidly when exposed to theatmosphere. More particularly, it relates to a container or package oftransparent, non-fibrous,

synthetic sheet or film that is eminently suited for such a use and forkindred uses.

Coffee has very definite characteristics not.

possessed by other food commodities. can be used, it must be roasted andground to a particular fineness. During the roasting operation, thereare developed in the coffee certain aromatic and vegetable or fixedoils. The aromatic oils'are volatile and pass very quickly into theatmosphere unless some means are provided to prevent such evaporation.The vegetable or fixed oils, on the other hand, readily become rancidwhen exposed to the oxygen-in the air. As a result, roasted coffee,particularly when ground, rapidly loses most of its desirable propertiesif exposed to the atmosphere.

It has been common practice to protect ground, roasted coffee bypackaging it under vacuum in glass or metal containers. However, thesecontainers are relatively expensive and their weight adds considerablyto the cost of their transportation.

It has therefore been proposed to package the ground material in afiexible, light-weight bagv or container made of a coated paper or asynthetic film. Among the synthetic films that have been mentioned forsuch use are regenerated cellulose, both the untreated andmoisture-proof variety, and various rubber derivatives including rubberhydrochloride.

To be suitable for use in the storage or shipment of ground coffee, sucha light-weight, flexible container must be highly impermeable to gases,including the volatile, aromatic gases of coffee and oxygen or air. Itmust be strong and sufiiciently tough to resist puncturing by thesharp-cornered coffee granules, and it should preferably be sufficientlyrigid so as not to require the presence of an external supporting means,such as a cardboard cover or carton. It should also be sufilcientlyflexible and durable at low temperatures to permit exposure to winteratmospheres. Moreover, to permit its manufacture on existing types ofpackaging machinery, the

container must be prepared from a material that is capable of beingheatsealed. Of course, the

completed package must be stable to light and Before it have beenproposed for use with coffee all fail to meet oneor more of theserequirements. For example, containers prepared from coated papersflorfilms of regenerated cellulose are generally not sufiicientlyimpermeable to oxygen or air at the high relative humidities oftenencountered. Furthermore, especially in the case of regeneratedcellulose, the containers are not sufficiently flexible at lowtemperatures, nor are they sufficiently tough to resist puncturing bythe coffee granules.

Those containers that have been prepared from rubber derivatives, e. g.rubber hydrochlorides, on the other hand, are relatively unstable andtend to decompose on exposure to sunlight. Moreover, they are sothermoplastic that they tend to lose their shape and open at the pointof sealing when exposed to high summer temperatures. The impermeabilityto oxygen of this rubber hydrochloride sheeting is not as high asdesired.

It.is,therefore, the principal object of this invention to provide a bagor like container or packageformed from a transparent, non-fibrous,synthetic sheet material, which container meets all of theabove-mentioned requirements and is suitable for use with substancessuch as ground coffee, that are deleteriously affected by exposure toair. Other objects will appear hereinafter.

The objects of this invention are accomplished, in general, by a packageprepared from a film comprising a partial acetal of polyvinyl alcohol,wherein from 12% to 55% of the available hydroxyl groups of thealcohol'have been reacted with an aliphatic aldehyde containing shouldhave a butyral content of from 23.5 to

33.7%). With aldehydes of lower molecular weight than butyraldehyde, i.e. formaldehyde, acetaldehyde, propionaldehyde, it is preferred thatfrom 40 to 55% of the available hydroxyl groups of polyvinyl alcoholhave been reacted with the aldehyde. With aldehydes of higher molecularweight than butyraldehyde, i. e. amylic aldehyde or hexaldehyde, it ispreferred that from 12 to 40% of the available hydroxyl groups ofpolyvinyl alcohol have been reacted with the aldehyde.

Although the; range of compositions given above as satisfactory forthese films is rather .notsufllciently thermoplastic to permit their usein a normal heat-sealing operation. on the other hand, if the acetalcontent is higher than that provided by the invention, theimpermeability of the films to oxygen and air is impaired.

The polyvinyl partial acetals suitable for the purposes of thisinvention are preferably prepared by the treatment of polyvinyl alcohol(obtained by the complete hydrolysis of polyvinyl acetate) with acontrolled amount of the desired aldehyde, in the presence of a suitablecatalyst, such as sulfuric acid, an organic sulfonic acid, etc. Theycan, however, also be prepared by the partial hydrolysis of a more orless completely acetalized polyvinyl alcohol, for example, by thecontrolled hydrolysis of a polyvinyl butyral having a butyral content offrom 40 to 50%. (The completely substituted polyvinyl butyral has abutyral content of 50.1%.) The formation of sheets or film from thesepartial acetals of polyvinyl alcohol is described in U. S. Patent Nos.2,044,730, 2,045,130, 2,120,628, and 2,253,078.

The packages of this invention are preferably prepared from pre-formedsheets of the abovementioned particular polyvinyl partial acetals by theuse of conventional types of package-making machinery whereby to formcontainers of any desired design, such as flat, square, round, satchelbottom, or automatic bags, wrappings, cartontype containers, etc.However, such a method of manufacture is not essential to the inventionand the polyvinyl partial acetals can, if desired, be cast from solutiondirectly in the form of a tubular structure, whose open ends aresubsequently closed by a heat-sealing operation; or they can be directlyformed into a cap-like structure comprising a tubular member openat onlyone end, this end being subsequently sealed after the introduction ofthe coffee or other material to be v packaged.

solution and the precipitated polyvinyl butyral is filtered off, washedand dried. Upon analysis, the

' dried product shows a butyral content of 30.3%-

corresponding to a substitution of 48% of the available hydroxyl groupsof the polyvinyl alcohol. Q

The product is then dissolved in a mixture of 80 parts of methanol and20 parts water to form a 15% solution, the solution being cast onto aheated plate to form a film of polyvinyl partial butyral 0.002 inchthick. The film is then formed into an open-mouthed bag in theconventional manner, filled with freshly ground coffee and sealed undervacuum in accordance with known procedures. The package isself-supporting and because of its transparency the condition of thecoffee within it can be readily noted. The package, which is quitefirmly packed, resists puncturing and can be handled roughly and evendropped from a height of several feet without rupturing. At the end oftwo months, the bag was opened and the cofiee examined. It did notappear to have lost any of its original aroma, nor did it appear to berancid or to have otherwise deteriorated.

In a tumble test, wherein a similar bag is filled with 240 grams of riceand dropped repeatedly generated cellulose and cellulose acetate andtested in this manner broke after being dropped 80 and 20 times,respectively.

Films of the polyvinyl partial acetals employed in this invention,particularlythose films that possess a thickness of not more than 3mils, are

I flexible even at low temperatures and do not necessarily require thepresence of a softener or plasvalue and containers possessing thickerorthinner walls are within the scope of the invention. Of course, theimpenetrability of the package to air and other media varies directlywith the wall thickness and this factor must be taken into account indesigning the package.

The invention is further illustrated by the following example of apreferred embodiment wherein parts are by weight unless otherwiseindicated.

- Example tained by the complete hydrolysis of 172 parts of polyvinylacetate are dissolved in 983 parts of water. The solution is maintainedat 12 C. and

0.88 part of sulfuric acid and 0.88 part of Aerosol O. T. (a wettingagent) are added. Thirty-six parts of butyraldehyde are then added withstirring. At the end of 20 minutes the temperature is raised to 20 C.and the solution is stirred at this temperature for one hour. Thetemperature of the solution is then raised at 30 minute intervals withconstant stirring to 30 and 40 C. and finally to 65 C. 0.88 part ofsulfuric acid dissolved in 100 parts of water is then added and stirringis continued for another 30 minutes. Aqueous caustic is then added toneutralize the ticizer. However, such a material, for example glycerin,can be incorporated in the film. In the case of a package for use withcoffee and prepared from a film 2 mils thick, a plasticizer content ofapproximately 20% of the film weight is preferred. Satisfactory resultscan, however, also be obtained with plasticizer contents of greater orlower value.

The containers of this invention are admirably suited for the packagingof freshly ground cofiee. However, they are not so limited." They canalso be used for the protection of other foodstuffs, such as powderedwhole milk, shortenings, etc., or objects that must be protected fromthe deteriorating influence of the atmosphere. Moreover, because thepackages of this invention are highly impermeable to substances such asoils, greases, etc. which cannot normally be packaged in flexiblecontainers, these packages may also be used for the storing and shippingof such substances. 0n the other hand, the packages of this inventioncan also be used as garment covers, etc., or the films may be used as aholland cloth substitute for the protection of articles such asunvulcanized rubber.

This invention provides a light-weight, heatsealable container that iseminently suited for the protection of foodstuffs such'as ground,roasted coffee, that are adversely affected by exposure to theatmosphere. The package is highly impermeable to gases, such as air,aromatic vapors and the like, and to liquids, such as water, oils,hydrocarbons, etc. The package is tough, strong and highly flexible atboth ordinary and low temper atures. It can withstand rough handlingduring storage or shipment. It is not affected by exposure to sunlight.It is sufficiently thermoplaspackage-manufacturing and heat-sealingapparatus. However, it does not soften or weaken on exposure to summertemperatures.

As many apparently widely difierent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A container suitable for the packaging of coffee, formed essentiallyof a film of a partial acetal of polyvinyl alcohol wherein from 12% to55% of the available hydroxyl groups of polyvinyl alcohol have beenreacted with an aliphatic aidehyde containing from'one to six carbonatoms.

2. A container suitable for the storage and shipment of freshly groundcofiee, formed essentially of a film of a partial butyral of polyvinylalcohol wherein from 12% to 55% of'the available hydroxylgroups ofpolyvinyl alcohol have been reacted with butyraldehyde.

3. A container suitable for the storage and shipment of freshly groundcofiee, formed essentially of a film of a partial butyral ofpolyvinylalcohol having a combined butyral content of shipment of freshly groundcoffee, formed essentially of a film of a partial butyral of polyvinylalcohol having a combined butyral content of from 23.5% to 33.7%, saidfilm having a thickness of about 2 mils.

5. A container suitable for the packaging of coffee, formed essentiallyof a plasticized film of a partial acetal of polyvinyl alcohol whereinfrom 12% to of the available hydroxylgroups of polyvinyl alcohol havebeen reacted with an aliphatic aldehyde containing from one to sixcarbon atoms, saidfilm containing about 20% by weight of glycerin.

LLOYD LYN LEACH;

REFERENCES CITED The following references are of record in the file -ofthis. patent:

UNITED STATES PATENTS

